Glass for information recording medium substrate, glass substrate for information recording medium and magnetic disk

ABSTRACT

To provide glass for an information recording medium substrate, which is excellent in the acid resistance and weather resistance. 
     Glass for an information recording medium substrate, which comprises, as represented by mol % based on the following oxides, from 61 to 72% of SiO 2 , from 3 to 12% of Al 2 O 3 , from 0 to 14.3 of Li 2 O, from 0 to 22% of Na 2 O, from 0 to 22% of K 2 O, from 4 to 13% of MgO, from 0 to 6% of TiO 2  and from 0 to 5% of ZrO 2 , provided that the total content of Li 2 O, Na 2 O and K 2 O (R 2 O) is from 8 to 22%, the ratio of the content of Li 2 O to R 2 O (Li 2 O/R 2 O) is at most 0.52, the ratio of the content of Na 2 O to R 2 O (Na 2 O/R 2 O) is at least 0.35, or the ratio of the content of K 2 O to R 2 O (K 2 O/R 2 O) is at least 0.45.

The present invention relates to glass to be used for an informationrecording medium substrate such as a magnetic disk (hard disk), a glasssubstrate for an information recording medium and a magnetic disk.

Glass substrates are widely used as substrates for information recordingmedium, particularly for magnetic disks, and a commercially availableglass substrate has been known, which has a composition comprising, asrepresented by mol %, SiO₂: 65.4%, Al₂O₃: 8.6%, Li₂O: 12.5%, Na₂O: 10.5%and ZrO₂: 3.0%. This commercially available glass is subjected tochemical strengthening treatment for use.

On the other hand, Patent Document 1 proposes a substrate glass for amagnetic disk, which is not subjected to chemical strengtheningtreatment.

Patent Document 1: JP-A-2002-358626 (Tables 1 to 14)

Since an acid having a low pH is used in a step of polishing or washinga glass substrate for a magnetic disk, the glass substrate for amagnetic disk is required to be free from surface roughening in thepolishing step or washing step at a low pH, i.e. to have acidresistance. Further, by using an acid having a low pH, it is possible toimprove the polishing rate or the performance to remove defects in thewashing step. However, in the case of glass having poor acid resistance,if an acid having a low pH is used, the polishing rate becomes low, ordefects tend to remain after washing to deteriorate the quality.

A glass substrate for a magnetic disk is required to have a propertysuch that a film such as a base film, a magnetic film or a protectivefilm, which is formed on the substrate, is prevented from peeling due toremarkable change of a surface condition during storage, namely it isrequired to have weather resistance. Alkali metal components such as Li,Na and K are widely used as a glass melt accelerator. However, suchcomponents are selectively extracted from glass by moisture in air, andthey are finally reacted with a component such as carbonic acid gas orsulfur dioxide gas in air and attach on a glass surface in the form ofan alkali metal carbonate or an alkali metal sulfate (white stain).Therefore, it is required to prevent such a reaction.

Further, if an alkali metal component diffuses to a magnetic film, aphenomenon such that recorded information is erased tends to occur.Therefore, there is a problem that reliability of recording medium isimpaired.

The present inventors conducted the after-mentioned weather resistancetest on the above-mentioned commercially available chemicallystrengthened glass, and the result was that the total precipitationamount C_(R) of Li, Na and K was 3.5 nmol/cm², (after-mentioned Example123). With one not chemically strengthened, C_(R) was 18.3 nmol/cm²(after-mentioned Example 124). With one not chemically strengthened, theweather resistance was low, and it is evident that the weatherresistance can be improved by the chemical strengthening treatment. Thatis, it is considered that this glass can be made useful as a glasssubstrate for a magnetic disk for the first time by the chemicalstrengthening treatment, and the reason is considered to be such thatthe amount of an alkali component having a large ion radius increases onthe glass surface along with the chemical strengthening treatment, andthe mobility is reduced. However, there are problems such that thechemical strengthening treatment increases the number of manufacturingsteps, thus leading to an increase of cost, and the substrate surfacetends to be stained by the chemical strengthening treatment.

On the other hand, most of the compositions exemplified in PatentDocument 1 contain at least 1 mol % of B₂O₃ in addition to an alkalimetal component. B₂O₃ is added in order to e.g. lower the brittleness ofglass, lower the specific gravity or improve the melting property ofglass. However, if B₂O₃ coexists with an alkali metal component, analkali metal borate compound having an extremely low vapor pressure isformed, and the alkali metal borate component volatilizes and diffusesfrom the glass melt vigorously.

FIG. 1 shows a vapor pressure curve of a boron compound calculated fromthermodynamic data disclosed in Malcolm W. Chase, Jr., NIST-JANAFThermochemical Tables, (U.S.A.), fourth edition, the American ChemicalSociety and American Institute of Physics, Year 1998, p. 242-274. Vaporpressure P was calculated from the free energy difference ΔG between gasphase and condensed phase at each temperature by the following formula.Results are shown on FIG. 1.

ΔG=RTlnP

Here, R is a gas constant.

It is evident from FIG. 1 that the vapor pressure of the alkali compoundof boron is by far higher than that of B₂O₃. Due to such a phenomenon,non-homogeneity such as striation occurs, and the quality of glassdeteriorates, and at the same time, there are problems such thatvolatized materials are condensed on refractories used for a glassmelting furnace, and the refractory strength is thereby substantiallylowered, and enormous cost is required to recover the volatizedsubstances.

Further, in order to study the influence of the content of B₂O₃ onvolatilization of alkali metal components from glass, each glass of theafter mentioned Examples 29, 137 and 138 was put in a platinum crucibleand left for 23 hours at 1,600° C., and the amount of Li₂O and theamount of Na₂O in the glass were analyzed by ICP-MS before and afterleaving it in the platinum crucible. Further, the contents of B₂O₃ inthe glass of Examples 29, 137 and 138 were 0 mol %, 1 mol % and 1.5 mol%, respectively.

As a result, the reduced amounts of Li₂O (absolute amounts) before andafter leaving the glass of Examples 29, 137 and 138 in the platinumcrucible were 0.0 mass %, 0.1 mass % and 0.1 mass %, respectively. Thereduced amounts of Na₂O (absolute amount) were 0.4 mass %, 0.8 mass %and 0.9 mass %, respectively. That is, between Example 29 wherein B₂O₃was not contained and Examples 137 and 138 wherein at least 1 mol % ofB₂O₃ was contained, the reduced amount of Na₂O was remarkably different.

Further, in Patent Document 1, five examples of containing no B₂O₃ areshown. However, in each of such examples, the content of alkali metalcomponents in glass was large, and C_(R) was thereby considered to be atleast 12 nmol/cm², and it is considered that alkali metals tend todiffuse into a magnetic film, and reliability is low. Further, the aftermentioned Example 125 corresponds to the glass of Example 63 in PatentDocument 1, and the after mentioned nitric acid etching rate was 181nm/h. Therefore, it is likely that surface roughening results in apolishing or washing step at a low pH, and the quality deteriorates.

The present inventors have considered that such problems occur due toglass which shows a high nitric acid etching rate in the acid resistancetest and a large amount of precipitation of alkalis in the weatherresistance test. Thus, the present invention has been accomplished inorder to solve such a problem without carrying out a chemicalstrengthening treatment and without incorporating a large amount ofB₂O₃.

MEANS TO ACCOMPLISH PROBLEMS

The present invention provides glass for an information recording mediumsubstrate, which comprises, as represented by mol % based on thefollowing oxides, from 61 to 72% of SiO₂, from 3 to 12% of Al₂O₃, from 0to 14.3 of Li₂O, from 0 to 22% of Na₂O, from 0 to 22% of K₂O, from 4 to13% of MgO, from 0 to 6% of TiO₂ and from 0 to 5% of ZrO₂, provided thatthe total content of Li₂O, Na₂O and K₂O (R₂O) is from 8 to 22%, theratio of the content of Li₂O to R₂O (Li₂O/R₂O) is at most 0.52, theratio of the content of Na₂O to R₂O (Na₂O/R₂O) is at least 0.35, or theratio of the content of K₂O to R₂O (K₂O/R₂O) is at least 0.45. Here, forexample “comprises from 0 to 14.3 of Li₂O” means that although Li₂O isnot essential, Li₂O may be contained up to 14.3%.

Further, the present invention provides the above glass for aninformation recording medium substrate, wherein Al₂O₃ is from 3 to 11%,and R₂O is from 10 to 22%.

Further, the present invention provides the above glass for aninformation recording medium substrate, wherein SiO₂ is from 62 to 71%,Al₂O₃ is from 4 to 10%, Li₂O is from 0 to 13%, Na₂O is from 0 to 20%,K₂O is from 0 to 20%, MgO is from 5 to 12%, TiO₂ is from 0 to 5%, ZrO₂is from 0 to 5%, and R₂O is from 11 to 20%.

Further, the present invention provides the above glass for aninformation recording medium substrate, wherein SiO₂ is from 63 to 70%,Al₂O₃ is from 5 to 9%, Li₂O is from 0 to 12.4%, Na₂O is from 0 to 19%,K₂O is from 0 to 19%, MgO is from 5 to 11%, TiO₂ is from 0 to 4%, ZrO₂is from 0 to 4%, and R₂O is from 13 to 19%.

Further, the present invention provides the above glass for aninformation recording medium substrate, which contains neither CaO, SrOnor BaO, which contains at least one of CaO, SrO and BaO in the totalcontent of at most 3%, or which contains from 0 to less than 5% of Li₂Oand from more than 2% to 8% of CaO.

In the above glass, the first and second embodiments of glass, namelythe glass for an information recording medium substrate, wherein thetotal content of CaO, SrO and BaO (CaO+SrO+BaO) is from 0 to 3% ispreferred when it is desired to increase the specific modulus and theaverage linear expansion coefficient (hereinafter, glass of the firstand second embodiments of glass is referred to as “glass A”).

The glass of the third embodiment, namely the glass for an informationrecording medium substrate wherein Li₂O is from 0 to less than 5%, andCaO is from more than 2% to 8% is preferred when it is desired to makethe glass transition temperature to be high (hereinafter, the glass ofthe third embodiment is referred to as “glass B”).

Further, the present invention provides glass for an informationrecording medium which contains no B₂O₃, or contains less than 1% ofB₂O₃.

Further, the present invention provides a glass substrate for aninformation recording medium which is made of the above glass for aninformation recording medium substrate.

Further, the present invention provides a magnetic disk having amagnetic recording layer formed on such a glass substrate for aninformation recording medium.

Further, the present invention provides the followings including some ofthe above-mentioned features.

1. Glass for an information recording medium substrate, which comprises,as represented by mol % based on the following oxides, from 61 to 72% ofSiO₂, from 3 to 12% of Al₂O₃, from 0 to 14.3 of Li₂O, from 0 to 22% ofNa₂O, from 0 to 22% of K₂O, from 4 to 13% of MgO, from 0 to 6% of TiO₂and from 0 to 5% of ZrO₂, provided that the total content of Li₂O, Na₂Oand K₂O (R₂O) is from 8 to 22%, the ratio of the content of Li₂O to R₂O(Li₂O/R₂O) is at most 0.52, the ratio of the content of Na₂O to R₂O(Na₂O/R₂O) is at least 0.35, or the ratio of the content of K₂O to R₂O(K₂O/R₂O) is at least 0.45.

2. The glass for an information recording medium substrate according tothe above 1, wherein the ratio of Li₂O/R₂O is at most 0.5, or the ratioof Na₂O/R₂O is at least 0.4.

3. The glass for an information recording medium substrate according tothe above 1 or 2, wherein the total content of TiO₂ and ZrO₂ (TiO₂+ZrO₂)is from 0 to 8%.

4. The glass for an information recording medium substrate according toany one of the above 1 to 3, which contains no B₂O₃ or contains lessthan 1% of B₂O₃.

5. The glass for an information recording medium substrate according toany one of the above 1 to 4, wherein the difference obtained bydeducting the content of Al₂O₃ from the content of SiO₂ exceeds 53%.

6. The glass for an information recording medium substrate according toany one of the above 1 to 5, wherein the difference obtained bydeducting the content of Li₂O from the content of K₂O is at most 9%.

7. The glass for an information recording medium substrate according toany one of the above 1 to 6, wherein R₂O is at least 10%.

8. The glass for an information recording medium substrate according toany one of the above 1 to 6, wherein SiO₂ is from 62 to 71%, Al₂O₃ isfrom 4 to 12%, Li₂O is from 0 to 12.4%, Na₂O is from 0 to 20%, K₂O isfrom 0 to 19%, MgO is from 5 to 12%, TiO₂ is from 0 to 5%, ZrO₂ is from0 to 4%, and R₂O is from 11 to 20%.

9. The glass for an information recording medium substrate according toany one of the above 1 to 8, wherein the content of Al₂O₃ is at most11%.

10. The glass for an information recording medium substrate according toany one of the above 1 to 6, wherein SiO₂ is from 63 to 70%, Al₂O₃ isfrom 5 to 9%, Li₂O is from 0 to 10.2%, Na₂O is from 0 to 19%, K₂O isfrom 0 to 12.8%, MgO is from 5 to 11%, TiO₂ is from 0 to 4%, ZrO₂ isfrom 0 to 4%, and R₂O is from 13 to 19%.

11. The glass for an information recording medium substrate according toany one of the above 1 to 10, which contains neither CaO, SrO nor BaO.

12. The glass for an information recording medium substrate according toany one of the above 1 to 10, which contains at least one of CaO, SrOand BaO in the total content of at most 3%.

13. The glass for an information recording medium substrate according toany one of the above 1 to 6, wherein Al₂O₃ is from 3 to 11%, Li₂O isfrom 0 to less than 5%, Na₂O is from 0 to 13%, K₂O is from 0 to 12%, MgOis from 4 to 11%, R₂O is from 8 to 17%, and CaO is from more than 2% to8%.

14. The glass for an information recording medium substrate according toany one of the above 1 to 6, wherein SiO₂ is from 61 to 71%, Al₂O₃ isfrom 4 to 11%, Li₂O is from 0 to 4.5%, Na₂O is from 0 to 12%, K₂O isfrom 0 to 10%, MgO is from 4 to 9%, and CaO is from 2.5 to 7%.

15. The glass for an information recording medium substrate according tothe above 13 or 14, wherein ZrO₂ is from 0.5 to 3%.

16. The glass for an information recording medium substrate according toany one of the above 1 to 15, which has a Young's modulus of at least 75GPa and a specific modulus of at least 28 MNm/kg.

17. The glass for an information recording medium substrate according toany one of the above 1 to 16, which has a glass transition temperatureof at least 500° C.

18. The glass for an information recording medium substrate according tothe above 13, 14 or 15, which has a Young's modulus of at least 76 GPa,a specific modulus of at least 30 MNm/kg and a glass transitiontemperature of at least 590° C.

19. The glass for an information recording medium substrate according toany one of the above 1 to 18, which has an average linear expansioncoefficient of at least 56×10⁻⁷/° C. in a temperature range of from −50to 70° C.

20. The glass for an information recording medium substrate according toany one of the above 1 to 19, wherein (T_(L)−T₄)<50° C., where T_(L) isthe liquidus temperature, and T₄ is the temperature at which theviscosity becomes 10⁴ dPa·s.

21. The glass for an information recording medium substrate according toany one of the above 1 to 20, which has a density of at most 2.60 g/cm³.

22. A glass substrate for an information recording medium, which is madeof the glass for an information recording medium substrate as defined inany one of the above 1 to 21.

23. The glass substrate for an information recording medium according tothe above 22, wherein when immersed in 0.01 N nitric acid at 25° C., theetching rate of glass is at most 0.3 nm/h.

24. The glass substrate for an information recording medium according tothe above 22 or 23, wherein when the glass is left under a steamatmosphere at 120° C. at 0.2 MPa for 20 hours, C_(R)=C_(Li)+C_(Na)+C_(K)is at most 12 nmol/cm², where C_(Li), C_(Na) and C_(K) are the amountsof Li, Na and K which precipitate on a surface of the glass,respectively.

25. A magnetic disk having a magnetic recording layer formed on theglass substrate for an information recording medium as defined in theabove 22, 23 or 24.

EFFECTS OF THE INVENTION

According to the present invention, glass for an information recordingmedium substrate, which has a high acid resistance can be obtained,whereby surface roughening can be prevented in a polishing step or awashing step under a low pH.

Further, the polishing rate of a glass substrate for an informationrecording medium can be improved, whereby the efficiency of thepolishing step can be improved.

Further, defects formed in the washing step can be reduced, and it ispossible to obtain a high quality glass substrate for an informationrecording medium.

Further, without carrying out a chemical strengthening treatment, it ispossible to obtain glass for an information recording medium substrate,wherein the total alkali precipitation amount after the weatherresistance test is low. Therefore, a film formed on the substrate suchas a base film, a magnetic film or a protective film is prevented frompeeling.

Further, it is possible to prevent alkalis from diffusing to a magneticfilm, and highly reliable recoding medium can be obtained.

Further, without carrying out a chemical strengthening treatment, aglass substrate for an information recording medium can be produced,whereby the number of process steps can be reduced, and the problem ofstain on the substrate surface after the chemical strengtheningtreatment can be solved.

Further, it is possible to obtain glass for an information recordingmedium substrate which has a high Young's modulus and a high specificmodulus. Therefore, warpage, deflection or fluttering during diskrotation can be prevented, whereby a recording medium having a highrecording density can be obtained.

Further, it is possible to obtain glass for an information recordingmedium substrate having a low density, whereby the motor load duringdisk rotation can be lowered, and it is possible to accomplish reductionof the power consumption.

Further, it is possible to obtain glass for an information recordingmedium substrate which has a high linear expansion coefficient.Therefore, matching in thermal expansion with other drive members madeof metal becomes better, the stress caused by a temperature changebecomes low, and substrate fracture, etc. are prevented.

Further, it is possible to obtain glass for an information recordingmedium substrate which has a low liquidus temperature, as compared withthe temperature at which the viscosity becomes 10⁴ dPa·s. Therefore,continuous forming is possible by e.g. a float process, a fusion methodor a down draw method, whereby mass production is possible.

Further, it is possible to obtain glass for an information recordingmedium substrate which has a high glass transition temperature.Therefore, the temperature for heat treatment which is carried out afterforming a magnetic film on the substrate can be set high, whereby it ispossible to obtain an information recording medium having a highrecording density.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the relationship between the temperature and the vaporpressures of B₂O₃ and an alkali compound of boron.

FIG. 2 shows the relationship between the ratios of alkali oxides(Li₂O/R₂O, Na₂O/R₂O and K₂O/R₂O) and C_(R). Numerical values atrespective points are C_(R) (unit: nmol/cm²). At the top point of Li,Li₂O/R₂O=1. At the top point of Na, Na₂O/R₂O=1. At the top point of K,K₂O/R₂O=1.

FIG. 3 shows the relationship between Na₂O/R₂O and C_(R), whenK₂O/R₂O=0. In the figure, y=56x²−77x+32 is a formula of an approximatecurve (y and x are C_(R) and Na₂O/R₂O, respectively, when K₂O/R₂O=0),and R² is a coefficient of determination.

BEST MODES FOR CARRYING OUT THE INVENTION

The density (d) of the glass for an information recording mediumsubstrate of the present invention (hereinafter referred to as the glassof the present invention) is preferably at most 2.60 g/cm³. If thedensity exceeds 2.60 g/cm³, motor load during disk rotation becomeshigh, and power consumption becomes large. Further, disk rotation islikely to be unstable. The density is preferably at most 2.54 g/cm³.

The glass of the present invention preferably has a Young's modulus (E)of at least 75 GPa and a specific modulus (E/d) of at least 28 MNm/kg.If E is lower than 75 GPa, or the specific modulus is lower than 28MNm/kg, the glass tends to warp or deflect during disk rotation, and itmay be difficult to obtain information recording medium having highrecording density. E is more preferably at least 76 GPa, and E/d is morepreferably at least 30 MNm/kg. E is particularly preferably at least 77GPa, and E/d is particularly preferably at least 30 MNm/kg.

The glass transition temperature (Tg) of the glass of the presentinvention is preferably at least 500° C. If Tg is lower than 500° C.,the temperature for the heat treatment for forming a magnetic layercannot be made to be sufficiently high, and it may be difficult toincrease the magnetic coercive force of the magnetic layer. Tg is morepreferably at least 510° C. In the case of the glass B, Tg is typicallyat least 590° C.

In the glass of the present invention, (T_(L)−T₄) is preferably lessthan 50° C., where T_(L) is the liquidus temperature, and T₄ is thetemperature at which the viscosity becomes 10⁴ dPa·s (workingtemperature). If (T_(L)−T₄) is 50° C. or more, it may be difficult tomanufacture the glass with a float process. (T_(L)−T₄) is morepreferably less than 40° C., particularly preferably less than 30° C.

The glass of the present invention preferably has a linear expansioncoefficient (α) of at least 56×10⁻⁷/° C. in a temperature range of from−50 to 70° C. If a is lower than 56×10⁻⁷/° C., the difference in thethermal expansion coefficient from other members such as a drive made ofmetal becomes large, and the substrate tends to fracture due to a stresscaused by temperature change. α is more preferably at least 58×10⁻⁷/° C.Typically, α is at most 100×10⁻⁷/° C.

When the glass substrate of the present invention for an informationrecording medium (hereinafter, referred to as “glass substrate of thepresent invention”) is left under steam atmosphere at 120° C. at 0.2 MPafor 20 hours, and the amount of Li, the amount of Na and the amount ofK, which precipitate on a surface of the glass are represented as C_(L),C_(Na) and C_(K) respectively, C_(R)=C_(Li)+C_(Na)+C_(K) is preferablyat most 12 nmol/cm². If C_(R) exceeds 12 nmol/cm², a film formed on thesubstrate, such as a base film, a magnetic film and a protective film islikely to be peeled. C_(R) is more preferably at most 11 nmol/cm².

It is preferred that the glass substrate of the present invention isexcellent in acid resistance such that the following nitric acid etchingrate is at most 0.3 nm/h. Otherwise, in a case where a strong acidhaving a pH of from 1 to 2 is used in a surface polishing step or finalwashing step in the production process of information recording medium,particularly the production process of substrate glass for a magneticdisk, the glass surface may be roughened or peel-broken. The nitric acidetching rate is more preferably at most 0.2 nm/h.

The nitric acid etching rate: A sample to be measured is prepared bypolishing a glass plate into mirror surface having a thickness of from 1to 2 mm and a size of 4 cm×4 cm. The sample is immersed in 0.01N nitricacid at 25° C. for 3 hours, and an Si amount eluted into the nitric acidis analyzed and measured by ICP-OES.

The nitric acid etching amount is calculated from the Si amount to beobtained, the SiO₂ content in the glass and the density of the glass.

Next, the composition of the glass of the present invention is explainedby employing mol % representation.

SiO₂ is a component for forming the glass structure and an essentialcomponent. If the content of SiO₂ is less than 61%, the acid resistanceand weather resistance become low, d tends to be large, or T_(L)increases whereby the glass becomes unstable. The content of SiO₂ ispreferably at least 62%, more preferably at least 63%. If the content ofSiO₂ exceeds 72%, the after-mentioned T₂ and T₄ raise, and it isdifficult to melt and form glass, E or E/d decreases, or a decreases.The content of SiO₂ is preferably at most 71%, more preferably at most70%.

Al₂O₃ has an effect to improve weather resistance and is an essentialcomponent. If the content of Al₂O₃ is less than 3%, the above effect isa little, E or E/d decreases, or Tg tends to be low. The content ofAl₂O₃ is preferably at least 4%, more preferably at least 5%. If thecontent of Al₂O₃ exceeds 12%, the acid resistance deteriorates, theafter-mentioned T₂ and T₄ raise, and it is difficult to melt and formglass, α decreases, or T_(L) becomes too high. The content of Al₂O₃ ispreferably at most 11%, more preferably at most 10%, typically at most9%.

The difference obtained by deducting the content of Al₂O₃ from thecontent of SiO₂ (SiO₂—Al₂O₃) preferably exceeds 53%. If SiO₂—Al₂O₃ is atmost 53%, the acid resistance may be insufficient.

Although Li₂O is not an essential component, Li₂O has an effect toincrease E, E/d or α, or improve the melting property of glass. Li₂O maybe contained up to 14.3%. If the content of Li₂O exceeds 14.3%, the acidresistance or weather resistance deteriorates, or Tg tends to be low.The content of Li₂O is preferably at most 13%, more preferably at most12.4%. When it is desired to increase E/d or α, for example in the glassA, the content of Li₂O is preferably at most 11%, more preferably atmost 10.2%, typically at most 9.5%. When it is desired to raise Tg, Li₂Ois not contained, or less than 5% of Li₂O may preferably be contained.The content of Li₂O is typically from 0 to 4.5%.

Although Na₂O is not is an essential component, Na₂O has an effect toincrease α or improve the melting property of glass, and Na₂O may becontained up to 22%. If the content of Na₂O exceeds 22%, the acidresistance or weather resistance deteriorates, or Tg tends to be low.The content of Na₂O is preferably at most 20%, more preferably at most19%, typically at most 18%. When it is desired to raise Tg, the contentof Na₂O is preferably at most 13%, more preferably at most 12%,typically at most 11%.

Although K₂O is not an essential component, K₂O has an effect toincrease a or improve the melting property of glass, and K₂O may becontained up to 22%. If the content of K₂O exceeds 22%, the acidresistance or weather resistance deteriorates, or E or E/d tends to below. The content of K₂O is preferably at most 20%, more preferably atmost 19%, particularly preferably at most 13%, further preferably atmost 12.8%, typically at most 12.5%. When it is desired to raise Tg, thecontent of K₂O is preferably at most 12%, more preferably at most 10%,typically at most 9%.

When it is desired to increase E/d, the difference obtained by deductingthe content of Li₂O from the content of K₂O (K₂O—Li₂O) is preferably atmost 9%, typically at most 8.5%.

If the total content of Li₂O, Na₂O and K₂O (R₂O) is less than 8%, αdecreases, or the melting property of glass deteriorates. R₂O ispreferably at least 9%, more preferably at least 10%. When it is desiredto increase E/d or α, for example in the glass A, R₂O is preferably atleast 11%, more preferably at least 13%. If R₂O exceeds 22%, the weatherresistance deteriorates. R₂O is preferably at most 20%, more preferablyat most 19%. In the glass B, R₂O is preferably at most 17%, morepreferably at most 15%.

FIG. 2 shows the relationship between the weather resistance and theratio of alkali oxide components. It is evident from FIG. 1 that C_(R)strongly depends on the ratio of alkali oxide components, and ifLi₂O/R₂O exceeds 0.52, Na₂O/R₂O is less than 0.35, and K₂O/R₂O is lessthan 0.45, the weather resistance deteriorates. Li₂O/R₂O is preferablyat most 0.5, or Na₂O/R₂O is preferably at least 0.4.

As mentioned above, Li₂O has an effect to increase E, E/d or α, and Na₂Oand K₂O have an effect to increase α, however, the weather resistancedeteriorates due to each of Li₂O, Na₂O and K₂O. On the other hand, inthe case of MgO, while maintaining the weather resistance, E, E/d or acan be increased. Therefore, R₂O can be decreased, and the weatherresistance of glass can be improved by adding MgO. As mentioned above,MgO has an effect to increase E, E/d or a or improve the meltingproperty of glass, while maintaining weather resistance. MgO is therebyan essential component. If the content of MgO is less than 4%, the aboveeffects are insufficient. The content of MgO is preferably at least 5%.If the content of MgO exceeds 13%, T_(L) is too high. The content of MgOis preferably at most 12%, more preferably at most 11%. When it isdesired to raise Tg, the content of MgO is preferably at most 9%.

CaO, SrO and BaO are not essential components. However, when it isdesired to increase a or improve the melting property of glass whilemaintaining the weather resistance, CaO, SrO or BaO may be contained.

When it is desired to increase E or E/d, to decrease d or to lowerT_(L), neither CaO, SrO nor BaO is preferably contained, or at least oneof CaO, SrO and BaO may be contained in the total content of at most 3%.The total content of CaO, SrO and BaO is preferably at most 2%,typically at most 1%.

For example, when it is desired that E is at least 76 GPa, E/d is atleast 30 MNm/kg, and Tg is at least 590° C., the content of Li₂O ispreferably from 0 to less than 5%, and the content of CaO is preferablyfrom more than 2% to 8%. If the content of Li₂O is at least 5%, or thecontent of CaO is at most 2%, Tg is difficult to be at least 590° C. Ifthe content of CaO exceeds 8%, E/d is difficult to be at least 30MNm/kg. The content of Li₂O is preferably from 0 to 4.5%, and thecontent of CaO is preferably from 2.5 to 7%, and the content of Li₂O istypically from 0 to 3%, and the content of CaO is typically from 3 to5.5%.

Although TiO₂ is not essential, it has an effect to increase E, E/d orTg or improve the weather resistance. Therefore, TiO₂ may be containedup to 6%. If the content of TiO₂ exceeds 6%, T_(L) tends to be too high,or a phase separation phenomenon tends to occur. The content of TiO₂ ispreferably at most 5%, more preferably at most 4.5%, particularlypreferably at most 4%. In a case where TiO₂ is contained, its content ispreferably at least 0.1%.

Although ZrO₂ is not essential, it has an effect to improve the weatherresistance, increase E or E/d, raise Tg or improve the melting propertyof glass. Therefore, ZrO₂ may be contained up to 5%. If the content ofZrO₂ exceeds 5%, d increases, or T_(L) tends to be too high. The contentof ZrO₂ is preferably at most 4%, typically at most 2.5%. When it isdesired to raise Tg, the content of ZrO₂ is typically at least 0.5% andpreferably at most 3%.

The total content of TiO₂ and ZrO₂ (TiO₂+ZrO₂) is preferably from 0 to8%. If the content of TiO₂+ZrO₂ exceeds 8%, d increases, T_(L) tends tobe too high, or a phase separation phenomenon tends to occur. Thecontent of TiO₂+ZrO₂ is more preferably at most 7%, particularlypreferably at most 6%, typically at most 5.5%. In a case where TiO₂ orZrO₂ is contained, the content of TiO₂+ZrO₂ is preferably at least 0.5%,more preferably at least 1%, particularly preferably at least 1.5%,typically at least 2%.

In the glass A, it is preferred that SiO₂ is from 62 to 71%, Al₂O₃ isfrom 4 to 12%, Li₂O is from 0 to 12.4%, Na₂O is from 0 to 20%, K₂O isfrom 0 to 19%, MgO is from 5 to 12%, TiO₂ is from 0 to 5%, ZrO₂ is from0 to 4%, and R₂O is from 11 to 20%.

Further, in the glass A, it is more preferred that SiO₂ is from 63 to70%, Al₂O₃ is from 5 to 9%, Li₂O is from 0 to 10.2%, Na₂O is from 0 to19%, K₂O is from 0 to 12.8%, MgO is from 5 to 11%, TiO₂ is from 0 to 4%,ZrO₂ is from 0 to 4%, and R₂O is from 13 to 19%; or SiO₂ is from 63 to70%, Al₂O₃ is from 5 to 9%, Li₂O is from 0 to 11%, Na₂O is from 0 to18%, K₂O is from 0 to 12.5%, MgO is from 5 to 9%, TiO₂ is from 0 to 4%,ZrO₂ is from 0 to 2.5%, and R₂O is from 13 to 19%.

In the glass B, it is preferred that Al₂O₃ is from 3 to 11%, Li₂O isfrom 5 to less than 5%, Na₂O is from 0 to 13%, K₂O is from 0 to 12%, MgOis from 4 to 11%, R₂O is from 8 to 17%, and CaO is from more than 2% to8%.

Further, in the glass B, it is more preferred that SiO₂ is from 61 to71%, Al₂O₃ is from 4 to 11%, Li₂O is from 0 to 4.5%, Na₂O is from 0 to12%, K₂O is from 0 to 10%, MgO is from 4 to 9%, and CaO is from 2.5 to7%.

The glass of the present invention basically comprises the abovecomponents, however, other components may be contained so long as theobject of the present invention is not impaired. In such a case, thetotal content of other components is preferably at most 5%, typically atmost 2%.

Further, a refining agent such as SO₃, Cl, As₂O₃, Sb₂O₃ or SnO₂ may becontained up to 2% in total.

Further, a colorant such as Fe₂O₃, CO₃O₄ or NiO may be contained up to2% in total.

Further, if B₂O₃ coexists with an alkali metal component, it is likelyto volatilize. Therefore, it is preferred not to contain B₂O₃. Even ifB₂O₃ is contained, its content is less than 1%, preferably less than0.5%.

Further, in a case where ZnO is contained, the total content representedby mass percentage of MgO and ZnO is preferably at most 7%, morepreferably at most 6%, further preferably at most 5%, particularlypreferably at most 4%.

Whether B₂O₃ or ZnO is contained or not, the ratio obtained by dividingthe total content of MgO and ZnO represented by mass percentage by theratio obtained by dividing the total content of SiO₂, Al₂O₃ and B₂O₃represented by mass percentage (MgO+ZnO)/(SiO₂+Al₂O₃+B₂O₃) is preferablyat most 0.08.

The glass substrate of the present invention is usually a circular glassplate.

The glass substrate of the present invention is typically used as aglass substrate for a magnetic disk.

The glass substrate for an magnetic disk is widely used for a 2.5 inchsubstrate (outside diameter of a glass substrate: 65 mm) used for laptopcomputers, etc. or a 1.8 inch substrate (outside diameter of a glasssubstrate: 48 mm) used for portable MP3 players, etc., and its market isexpanding year by year, while it is demanded to supply the glasssubstrate at low price.

Mass production of plate glass is widely carried out by a continuousforming method such as a float process, a fusion method or a down drawmethod. Since the glass of the present invention is glass which can beformed by a float process as mentioned above, the glass of the presentinvention is preferred for mass production.

The methods for producing the glass of the present invention and theglass substrate of the present invention are not particularlyrestricted, and various methods can be applied. For example, materialsof respective components to be usually used are measured and mixed so asto constitute the desired composition and then heat-melted in a glassmelting furnace. The glass is homogenized by bubbling, stirring, addinga refining agent or the like, then formed by a conventional method suchas a float process, a press method, a fusion method or a down drawmethod and annealed. Then, as a case requires, processing such asgrinding or polishing is carried out to form a glass substrate having apredetermined size and shape. The forming method is particularlypreferably a float process, which is suitable for mass production.Further, a continuous forming method other than a float process, namelya fusion method or a down draw method is also preferred.

Examples

Materials of respective components were measured and mixed so as toconstitute the compositions represented by mol % in the rows for fromSiO₂ to ZrO₂ or B₂O₃ in Tables 1 to 18 and melted in a platinum crucibleat a temperature of from 1,550 to 1,600° C. for 3 to 5 hours. At thetime of melting, a platinum stirrer was inserted in molten glass, andthe molten glass was stirred for 2 hours to homogenize glass. Then, themolten glass was flown out, formed into a plate and annealed to roomtemperature at a cooling rate of 1° C./minute. Further, in Tables, R₂Orepresents the total content (unit: mol %) of Li₂O, Na₂O and K₂O.

Glasses of Examples 1 to 117, 126 to 132, 137 and 138 are workingexamples of the present invention, and glasses of Examples 118 to 125and 133 to 136 are comparative examples. Further, glass of Example 126to 136 were produced by without carrying out the above mentionedmelting. Further, glass of Example 123 is the same as theabove-mentioned commercially available chemical strengthened glass, andit was produced by chemical strengthening of the glass of Example 124.

With respect to the glass plates thus obtained, density d (unit: g/cm³),the above-mentioned average linear expansion coefficient α (unit×10⁻⁷/°C.), Young's modulus E (unit: GPa), specific modulus E/d (unit: MNm/kg),glass transition temperature Tg (unit: ° C.), liquidus temperature T_(L)(unit: ° C.), temperature at which the viscosity becomes 10² dPa·s T₂(unit: ° C.), temperature at which the viscosity becomes 10⁴ dPa·s T₄(unit: ° C.), the above-mentioned C_(R) (unit: nmol/cm²), and theabove-mentioned nitric acid etching rate were measured by the followingmethods. The results are shown in Tables 1 to 18, and “-” in Tablesmeans “not measured”, and a value with “*” are an estimated value fromits composition.

Further, compositions of respective glasses represented by masspercentage are shown in Tables 19 to 36.

d: d was measured by Archimedes' method by using 20 to 50 g of glasshaving no bubble.

α: By using a differential thermal dilatometer and quartz glass as areference material, the degree of elongation of glass at a time ofraising the temperature from room temperature at a rate of 5° C./minutewas measured until the temperature at which glass softened, andelongation was no longer observed, namely the yield point, and anaverage linear expansion coefficient in a temperature range of from −50to 70° C. was calculated from the obtained thermal expansion curve.

E: With respect to a glass plate having a thickness of from 5 to 10 mmand a size of 3 cm×3 cm, E was measured by an ultrasonic pulse-echomethod.

Tg: By using a differential thermal dilatometer and quartz glass as areference material, the degree of elongation of glass at a time ofraising the temperature from room temperature at a rate of 5° C./minutewas measured until the yield point, and a temperature at a criticalpoint on the obtained thermal expansion curve was determined as a glasstransition temperature.

T_(L): Glass was pulverized by a mortar to glass particles having aparticle size of about 2 mm, the glass particles were lined up on aplatinum board and heat-treated in a temperature gradient furnace for 24hours. The highest temperature of the glass particles wherein crystalprecipitated was determined as a liquidus temperature. Further, forexample, “≧1150° C.” and “≦1050° C.” mean “at least 1,150° C.” and “atmost 1,050° C.” respectively.

T₂ and T₄: T₂ and T₄ were measured by a rotation viscometer.

C_(R): Both surfaces of a glass plate having a thickness of from 1 to 2mm and a size of 4 cm×4 cm were mirror-polished with cerium oxide andwashed with calcium carbonate and a detergent, and then the glass platewas put in a highly accelerated stress test system (unsaturated typepressure cracker EHS-411M, manufactured by ESPEC Corp.) and left under asteam atmosphere at 120° C. and 0.2 MPa for 20 hours. The tested sampleand 20 ml of ultra pure water were put in a washed plastic bag providedwith a zipper, a surface precipitate was dissolved with applyingultrasonic wave for 10 minutes, and respective alkali components ofeluates were quantified by using ICP-MS. The amount of such eluates wasconverted to mol and normalized with the surface area of the testsample.

Nitric acid etching rate: The nitric acid etching rate was observed bythe above-mentioned method (unit: nm/h). The results are shown in therow for “Acid resistance”.

The acid resistance is strongly influenced by Al₂O₃, and the lower theamount of Al₂O₃ is, the more the acid resistance improves. On the otherhand, the weather resistance is also strongly influenced by Al₂O₃, andthe lower the amount of Al₂O₃ is, the more the weather resistancedeteriorates. Further, the weather resistance is also stronglyinfluenced by alkali components, and when the total amount of alkalicomponents is reduced, or the ratio of alkali components is adjustedwithin a preferred range, the weather resistance improves. The totalamount of alkali components in the glass of the present invention isreduced, compared to Example 122, and the ratio of alkali components isadjusted within an appropriate range, whereby the deterioration of theweather resistance due to the reduction of Al₂O₃ is suppressed, and theacid resistance of the glass of the present invention is superior tothat of Example 122.

TABLE 1 Ex. 1 2 3 4 5 6 7 8 SiO₂ 66.0  66.0  66.0  66.0  65.0  64.0 66.0  66.0  Al₂O₃ 5.5 5.5 5.5 5.5 6.5 7.5 5.5 5.5 Li₂O 8.4 8.4 8.4 8.48.4 8.4 5.5 6.5 Na₂O 4.0 4.0 4.0 4.0 5.0 5.0 6.9 4.0 K₂O 4.6 4.6 4.6 4.64.6 4.6 4.6 6.5 MgO 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 TiO₂ 2.0 0  3.5 1.00  0  1.0 1.0 ZrO₂ 1.5 3.5 0  2.5 2.5 2.5 2.5 2.5 R₂0 17.0  17.0  17.0 17.0  18.0  18.0  17.0  17.0  Li₂0/R₂0  0.49  0.49  0.49  0.49  0.47 0.47  0.32  0.38 Na₂0/R₂0  0.24  0.24  0.24  0.24  0.28  0.28  0.41 0.24 K₂0/R₂0  0.27  0.27  0.27  0.27  0.26  0.26  0.27  0.38 d  2.50 2.53  2.47  2.51  2.51  2.52  2.52  2.51 α 69   69   73   69   73  72   75   73   E 83.5  85.7  83.6  84.2  83.3  83.8  81.7  82.2  Tg534   545   523   540   532   540   543   546   T_(L) 1000    ≧1150     1000    1100    ≦1050      E/d 33.4  33.9  33.8  33.5  33.2  33.3  32.4 32.7  T₂ 1493*   1501*   1488*   1497*   1494*   1501*   1529*   1538*  T₄ 1058*   1081*   1041*   1070*   1069*   1078*   1099*   1106*   C_(R)8.5 6.4 10.4  10.6  7.3 5.2 6.4 5.4 Acid  0.07  0.07  0.07  0.10  0.11 0.11  0.07*  0.09 resistance

TABLE 2 Ex. 9 10 11 12 13 14 15 16 SiO₂ 66.0  68.0  66.0  66.0  66.0 66.0  66.0  66.0  Al₂O₃ 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 Li₂O 5.1 7.4 5.78.5 8.5 5.1 3.4 3.4 Na₂O 8.0 3.5 5.7 0  8.5 11.9  11.9  10.2  K₂O 3.94.1 5.7 8.5 0  0  1.7 3.4 MgO 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 TiO₂ 1.01.0 1.0 1.0 1.0 1.0 1.0 1.0 ZrO₂ 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 R₂017.0  15.0  17.0  17.0  17.0  17.0  17.0  17.0  Li₂0/R₂0  0.30  0.49 0.33  0.50  0.50  0.30  0.20  0.20 Na₂0/R₂0  0.47  0.24  0.33 0   0.50 0.70  0.70  0.60 K₂0/R₂0  0.23  0.27  0.33  0.50  0.00  0.00  0.10 0.20 d  2.52  2.50  2.52  2.50  2.53  2.53  2.53  2.53 α 74   65   75  73   68   71   77   78   E 81.9  84.3  81.2  78.9  86.7  83.2  81.4 80.4  Tg 547   562   545   561   541   554   556   554   T_(L)≦1050      1150    ≦1050      1050    ≧1100      1050    1050   ≦1050      E/d 32.4  33.7  32.2  31.6  34.3  32.9  32.1  31.8  T₂1526*   1559*   1538*   1537*   1448*   1485*   1521*   1539*   T₄1097*   1117*   1107*   1104*   1028*   1062*   1095*   1110*   C_(R)5.2 6.1 5.9 6.1 5.7 5.7 5.3 4.6 Acid  0.07*  0.06  0.08  0.07*  0.06 0.07*  0.07*  0.07* resistance

TABLE 3 Ex. 17 18 19 20 21 22 23 24 SiO₂ 66.0  64.0  64.0  63.0  63.0 63.0  63.0  63.0  Al₂O₃ 5.5 5.5 7.5 7.5 7.5 8.5 7.5 7.5 Li₂O 1.7 9.4 8.06.5 5.9 8.4 7.8 5.9 Na₂O 15.3  4.5 10.9  11.3  11.3  10.0  10.0  11.3 K₂O 0  5.1 0  0  0  0.6 0.7 0  MgO 8.0 8.0 7.0 9.2 10.2  6.0 7.6 10.2 TiO₂ 1.0 1.0 0  0  0  2.5 2.0 0.5 ZrO₂ 2.5 2.5 2.5 2.5 2.0 1.0 1.5 1.5R₂0 17.0  19.0  19.0  17.8  17.3  19.0  18.4  17.3  Li₂0/R₂0  0.10  0.49 0.42  0.37  0.34  0.44  0.42  0.34 Na₂0/R₂0  0.90  0.24  0.58  0.63 0.66  0.53  0.54  0.66 K₂0/R₂0 0   0.27 0  0  0   0.03  0.04 0  d  2.53 2.53  2.52  2.54  2.53  2.51  2.52  2.52 α 78   75   72   72   72  74   72   72   E 79.0  84.2  85.8  85.8  84.7  85.1  85.6  84.5  Tg583   520   534   553   556   531   534   554   T_(L) <1000    1050   1100    1100    <1000    1100    E/d 31.2  33.3  34.0  33.8  33.5  33.9 33.9  33.6  T₂ 1522*   1435*   1452*   1451*   1456*   1463*   1444*  1454*   T₄ 1097*   1023*   1032*   1046*   1050*   1028*   1024*  1044*   C_(R) 8.5 7.9 5.7 4.5 4.4 7.0 8.1 6.2 Acid  0.07  0.06  0.06 0.12  0.12  0.16  0.14  0.11 resistance

TABLE 4 Ex. 25 26 27 28 29 30 31 32 SiO₂ 63.0  63.0  63.0  63.0  63.0 70.0  66.0  66.0  Al₂O₃ 7.5 7.5 7.5 7.5 7.5 5.5 5.5 5.5 Li₂O 5.9 5.9 5.95.9 5.9 6.4 1.7 0  Na₂O 11.3  11.3  11.3  11.3  11.3  3.1 8.5 17.0  K₂O0  0  0  0  0  3.5 6.8 0  MgO 10.2  10.2  8.7 7.7 6.7 8.0 8.0 8.0 TiO₂1.0 1.5 2.0 3.0 4.0 1.0 1.0 1.0 ZrO₂ 1.0 0.5 1.5 1.5 1.5 2.5 2.5 2.5 R₂017.3  17.3  17.3  17.3  17.3  13.0  17.0  17.0  Li₂0/R₂0  0.34  0.34 0.34  0.34  0.34  0.49  0.10 0  Na₂0/R₂0  0.66  0.66  0.66  0.66  0.66 0.24  0.50  1.00 K₂0/R₂0 0  0  0  0  0   0.27  0.40 0  d  2.51  2.50 2.53  2.54  2.54  2.49  2.52  2.54* α 73   72   72   71   71   58  82   80*  E 84.5  84.3  84.8  85.2  85.2  84.7  76.8  80.0* Tg 549  545   556   557   559   585   574   566*   T_(L) 1100    1080    1040   1000    ≧1200      ≦1100      E/d 33.7  33.7  33.5  33.6  33.5  34.1 30.4  31.5* T₂ 1452*   1450*   1474    1474    1479    1620*   1593*  1540*   T₄ 1038*   1033*   1044    1047    1042    1163*   1158*  1114*   C_(R) 7.0 8.9 5.1 4.9 4.5 4.5 6.9 9.2 Acid  0.13  0.12  0.13 0.12  0.12  0.18  0.06  0.07* resistance

TABLE 5 Ex. 33 34 35 36 37 38 39 40 SiO₂ 66.0  66.0  66.0  66.0  65.8 66.0  64.0  64.0  Al₂O₃ 5.5 5.5 5.5 5.5 11.0  10.0  11.0  10.0  Li₂O 0 0  0  4.3 3.0 0  4.8 4.8 Na₂O 8.5 12.8  4.3 0  13.5  14.0  12.0  12.0 K₂O 8.5 4.3 12.8  12.8  0  0  0  0  MgO 8.0 8.0 8.0 8.0 6.7 10.0  8.29.2 TiO₂ 1.0 1.0 1.0 1.0 0  0  0  0  ZrO₂ 2.5 2.5 2.5 2.5 0  0  0  0 R₂0 17.0  17.0  17.0  17.0  16.5  14.0  16.8  16.8  Li₂0/R₂0 0  0  0  0.25  0.18  0.00  0.29  0.29 Na₂0/R₂0  0.50  0.75  0.25 0   0.82  1.00 0.71  0.71 K₂0/R₂0  0.50  0.25  0.75  0.75 0  0  0  0  d  2.53*  2.54* 2.52*  2.51*  2.45  2.45  2.46  2.46 α 85*  83*  88*  81*  74   71  72   72   E 75.1* 77.6* 72.7* 75.9* 79.9  76.9  81.3  81.9  Tg 563*  564*   561*   551*   570*   596*   564*   557*   T_(L) ≦1150     1200    ≧1150      E/d 29.7* 30.6* 28.8* 30.3* 32.6  31.4  33.1  33.2 T₂ 1629*   1585*   1674*   1628*   1645*   1665*   1583*   1552*   T₄1191*   1153*   1229*   1185*   1169*   1202*   1126*   1105*   C_(R)6.7 7.7 6.4 4.4 2.0 3.9 2.5 3.1 Acid  0.07*  0.07*  0.07*  0.07*  0.17 0.12  0.22  0.18 resistance

TABLE 6 Ex. 41 42 43 44 45 46 47 48 SiO₂ 64.0  64.5  64.0  64.0  63.7 63.4  64.0  64.0  Al₂O₃ 9.5 9.5 9.5 9.1 9.1 9.4 10.0  8.0 Li₂O 4.8 3.84.0 5.2 5.5 5.5 5.8 5.8 Na₂O 11.5  12.0  12.3  11.5  11.5  11.5  11.5 11.5  K₂O 0  0  0  0  0  0  0  0  MgO 10.2  10.2  10.2  10.2  10.2 10.2  7.2 9.2 TiO₂ 0  0  0  0  0  0  0  0  ZrO₂ 0  0  0  0  0  0  1.51.5 R₂0 16.3  15.8  16.3  16.7  17.0  17.0  17.3  17.3  Li₂0/R₂0  0.29 0.24  0.25  0.31  0.32  0.32  0.34  0.34 Na₂0/R₂0  0.71  0.76  0.75 0.69  0.68  0.68  0.66  0.66 K₂0/R₂0 0  0  0  0  0  0  0  0  d  2.47 2.46  2.47  2.47  2.47  2.47  2.50  2.50 α 69   69   72   71   71  71   71   70   E 83.0  81.1  81.2  81.9  82.3  83.3  83.5  83.7  Tg559*   566*   560*   551*   547*   549*   566*   553*   T_(L) ≧1150     ≦1100      1050    E/d 33.6  32.9  32.9  33.2  33.4  33.8  33.4  33.4 T₂ 1539*   1564*   1547*   1520*   1508*   1511*   1553*   1491*   T₄1098*   1119*   1107*   1082*   1073*   1076*   1110*   1067*   C_(R)5.0  7.8*  8.4* 5.7 6.6 5.3 3.9 6.0 Acid  0.14  0.16*  0.17*  0.20  0.11 0.17  0.18  0.10 resistance

TABLE 7 Ex. 49 50 51 52 53 54 55 56 SiO₂ 64.0  64.0  64.0  64.0  64.0 64.0  64.0  64.0  Al₂O₃ 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 Li₂O 2.5 3.0 3.53.0 3.0 3.0 3.0 3.0 Na₂O 4.5 4.5 4.5 3.5 1.0 4.0 4.5 2.5 K₂O 5.0 5.5 6.05.0 8.0 4.0 4.5 6.0 MgO 6.5 6.5 6.5 6.5 6.5 7.0 7.0 6.8 CaO 5.5 4.5 3.55.5 5.0 5.5 3.0 5.3 TiO₂ 1.5 1.5 1.5 2.0 2.0 2.0 3.0 2.0 ZrO₂ 1.5 1.51.5 1.5 1.5 1.5 2.0 1.5 R₂0 12.0  13.0  14.0  11.5  12.0  11.0  12.0 11.5  Li₂0/R₂0  0.21  0.23  0.25  0.26  0.25  0.27  0.25  0.26 Na₂0/R₂0 0.38  0.35  0.32  0.30  0.08  0.36  0.38  0.22 K₂0/R₂0  0.42  0.42 0.43  0.43  0.67  0.36  0.38  0.52 d  2.54  2.53  2.52  2.54  2.53 2.54  2.55  2.54 α 68   70   71   67   70   64   67   68   E 81.8 81.8  81.1  82.6  80.4  83.9  83.0  82.0  Tg 625   603   593   631  640   632   633   636   T_(L) 1140    E/d 32.2  32.3  32.1  32.5  31.8 33.0  32.6  32.3  T₂ 1621*   1621*   1620*   1621*   1653*   1613*  1636*   1638*   T₄ 1191*   1186*   1182*   1191*   1216*   1187*  1203*   1201*   C_(R)  0.9*  1.1*  1.4*  0.7*  0.7*  0.7*  0.5*  0.7*Acid  0.16*  0.16*  0.16*  0.16*  0.25  0.16*  0.17  0.12 resistance

TABLE 8 Ex. 57 58 59 60 61 62 63 64 SiO₂ 64.0  63.0  62.0  62.0  64.0 64.0  64.0  64.0  Al₂O₃ 9.0 9.0 9.5 9.0 7.0 9.0 9.0 9.0 Li₂O 3.5 4.0 4.03.5 3.5 3.5 3.5 1.5 Na₂O 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 K₂O 6.0 6.0 6.56.0 6.0 6.0 6.0 6.0 MgO 7.0 7.5 7.5 7.0 7.0 5.0 7.0 7.0 CaO 3.0 3.0 3.03.0 3.0 3.0 3.0 3.0 TiO₂ 3.0 3.0 3.0 5.0 5.0 5.0 5.0 5.0 ZrO₂ 2.0 2.02.0 2.0 2.0 2.0 0  2.0 R₂0 12.0  12.5  13.0  12.0  12.0  12.0  12.0 10.0  Li₂0/R₂0  0.29  0.32  0.31  0.29  0.29  0.29  0.29  0.15 Na₂0/R₂0 0.21  0.20  0.19  0.21  0.21  0.21  0.21  0.25 K₂0/R₂0  0.50  0.48 0.50  0.50  0.50  0.50  0.50  0.60 d  2.54  2.55  2.55  2.57  2.55 2.55  2.51  2.55 α 67   68   69   75   68   70   69   65   E 82.6 83.4  82.8  83.3  82.2  81.7  80.5  80.4  Tg 635   623   626   635  618   629   619   687   T_(L) ≧1250      1200    E/d 32.5  32.7  32.4 32.4  32.2  32.0  32.1  31.5  T₂ 1646*   1615*   1610*   1612*   1597*  1658*   1639*   1691*   T₄ 1211*   1190*   1189*   1191*   1172*  1215*   1188*   1253*   C_(R)  0.5*  0.5*  0.4*  0.3*  0.6*  0.3*  1.0* 0.2* Acid  0.16*  0.18*  0.22*  0.21*  0.12*  0.16*  0.16*  0.16*resistance

TABLE 9 Ex. 65 66 67 68 69 70 71 72 SiO₂ 64.0  64.0  66.0  66.0  66.0 66.0  66.0  66.0  Al₂O₃ 9.0 9.0 7.0 7.0 7.9 8.0 7.6 7.5 Li₂O 3.5 3.5 3.53.5 3.0 3.0 3.4 3.0 Na₂O 0.5 2.5 2.5 2.5 3.5 3.5 2.4 3.5 K₂O 6.0 4.0 6.06.0 5.1 5.1 5.7 5.8 MgO 7.0 7.0 7.0 6.0 6.0 6.0 6.0 6.5 CaO 3.0 3.0 3.03.0 3.0 3.0 3.0 3.5 TiO₂ 5.0 5.0 3.0 4.5 3.8 3.9 4.5 2.0 ZrO₂ 2.0 2.02.0 1.5 1.8 1.5 1.5 2.2 R₂0 10.0  10.0  12.0  12.0  11.5  11.6  11.4 12.3  Li₂0/R₂0  0.35  0.35  0.29  0.29  0.26  0.26  0.30  0.24 Na₂0/R₂0 0.05  0.25  0.21  0.21  0.30  0.30  0.21  0.28 K₂0/R₂0  0.60  0.40 0.50  0.50  0.44  0.44  0.50  0.47 d  2.55  2.56  2.53  2.53  2.53 2.53  2.53  2.54 α 63   60   64   66   65   64   64   69   E 82.2 84.5  82.3  80.8  81.4  81.6  81.5  81.7  Tg 660   652   619   595  612   613   620   612   T_(L) 1190    1080    1150    1200    1100   1204    E/d 32.3  33.1  32.5  32.0  32.2  32.3  32.2  32.2  T₂ 1669*  1648*   1631*   1635*   1661*   1659*   1655*   1641*   T₄ 1233*  1215*   1192*   1188*   1211*   1208*   1205*   1202*   C_(R)  0.2* 0.2*  1.1*  1.1*  0.7*  0.8*  0.8*  1.1* Acid  0.16*  0.16*  0.09* 0.09*  0.10*  0.10*  0.09*  0.09* resistance

TABLE 10 Ex. 73 74 75 76 77 78 79 80 SiO₂ 66.0  67.6  67.9  67.5  68.1 66.0  66.0  66.0  Al₂O₃ 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.0 Li₂O 2.5 0.3 1.80  0.1 0  0.2 2.0 Na₂O 4.0 7.6 3.1 10.0  9.4 10.0  10.0  7.0 K₂O 5.8 3.26.0 1.7 2.2 3.9 3.2 4.4 MgO 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 CaO 4.0 4.04.0 4.0 4.0 4.0 4.0 4.0 TiO₂ 1.0 1.7 1.5 1.2 0.3 0.3 0.8 0.8 ZrO₂ 2.21.7 1.8 1.7 1.8 1.8 1.8 1.8 R₂0 12.3  11.0  10.9  11.6  11.8  13.9 13.4  13.4  Li₂0/R₂0  0.20  0.03  0.16 0   0.01 0   0.02  0.15 Na₂0/R₂0 0.33  0.69  0.29  0.86  0.80  0.72  0.75  0.52 K₂0/R₂0  0.47  0.29 0.55  0.14  0.19  0.28  0.24  0.33 d  2.54  2.52  2.51  2.52  2.51 2.52  2.53  2.53 α 68   65   66   67   68   77   76   71   E 81.3 79.8  79.7  79.1  78.8  77.5  78.6  81.0  Tg 613   652   637   653  646   627   625   594   T_(L) 1204    1100    1169    1100    1155   1100    1100    1100    E/d 32.1  31.6  31.7  31.4  31.4  30.7  31.1 32.1  T₂ 1636*   1677*   1699*   1657*   1683    1628*   1625*   1619*  T₄ 1200*   1227*   1242*   1209*   1221    1189*   1186*   1179*   C_(R) 1.3* 1.6 1.3 1.8 2.6  2.9*  2.4*  2.4* Acid  0.09*  0.07*  0.07*  0.07* 0.04  0.09*  0.09*  0.09* resistance

TABLE 11 Ex. 81 82 83 84 85 86 87 88 SiO₂ 66.0  66.0  65.9  67.0  67.0 67.0  67.0  66.5 Al₂O₃ 7.5 7.5 7.4 7.5 7.5 7.5 7.5 7.7 Li₂O 1.5 2.3 1.51.2 0.8 1.3 1.0 0.6 Na₂O 7.0 7.0 7.0 7.0 7.0 7.0 7.0 8.7 K₂O 4.1 4.6 3.84.3 4.1 3.6 4.0 2.2 MgO 6.5 6.5 6.4 7.0 7.0 7.0 7.0 7.5 CaO 4.0 4.0 4.04.0 4.5 4.5 4.5 4.0 TiO₂ 1.7 0.3 2.3 0.3 0.3 0.3 0.3 1.0 ZrO₂ 1.8 1.81.6 1.8 1.8 1.8 1.7 1.8 R₂0 12.6  13.9  12.3  12.4  11.9  11.9  12.0 11.6 Li₂0/R₂0  0.12  0.16  0.12  0.09  0.07  0.11  0.09 0.05 Na₂0/R₂0 0.56  0.50  0.57  0.56  0.59  0.59  0.58 0.75 K₂0/R₂0  0.33  0.33  0.31 0.34  0.34  0.30  0.33 0.19 d  2.53  2.52  2.53  2.52  2.52  2.52  2.522.53 α 70   72   68   69   69   68   69   67 E 80.8  80.5  80.9  79.8 79.8  80.6  79.9  81.0 Tg 611   583   610   613   626   616   623   637T_(L) 1100    1100    1122    1153    1144    1152    1163    ≦1160 E/d31.9  31.9  31.9  31.7  31.7  32.0  31.8  32.0 T₂ 1631*   1612*  1628*   1651*   1653*   1643*   1649*   1627 T₄ 1191*   1173*   1188*  1206*   1210*   1200*   1205*   1203 C_(R)  1.6*  3.0*  1.5*  2.3* 2.4 2.1*  2.1* 1.8 Acid  0.09*  0.09*  0.09*  0.08*  0.05  0.08*  0.08*0.06 Resistance

TABLE 12 Ex. 89 90 91 92 93 94 95 96 SiO₂ 66.7  66.8  67.0  66.2  66.5 66.4  66.8  66.8  Al₂O₃ 7.7 7.7 7.6 7.7 7.7 7.7 7.7 7.7 Li₂O 0.6 0.6 1.30.2 1.1 0.4 0.5 0.5 Na₂O 8.7 8.7 9.0 10.0  8.7 10.0  10.0  10.0  K₂O 2.22.2 2.0 0.7 2.2 0.8 0.8 0.8 MgO 7.0 7.0 6.6 7.5 7.5 7.5 7.5 7.5 CaO 4.54.5 4.0 4.5 4.0 4.5 4.5 4.0 TiO₂ 1.0 1.0 1.0 1.6 0.5 1.1 0.5 1.0 ZrO₂1.6 1.5 1.6 1.7 1.8 1.7 1.7 1.7 R₂0 11.6  11.6  12.3  11.0  12.1  11.1 11.4  11.4  Li₂0/R₂0  0.05  0.05  0.10  0.02  0.09  0.03  0.05  0.05Na₂0/R₂0  0.75  0.75  0.73  0.91  0.72  0.90  0.88  0.88 K₂0/R₂0  0.19 0.19  0.16  0.07  0.18  0.07  0.07  0.07 d  2.53  2.52  2.52  2.54 2.53  2.53  2.53  2.53 α 68   67   67   63   68   65   65   65   E80.6  79.8  80.1  81.2  81.5  81.3  81.3  80.9  Tg 635   635   617  653   618   645   638   639   T_(L) 1160    1164    ≦1160      1162   ≦1154      1154    E/d 31.9  31.6  31.8  32.0  32.3  32.1  32.2  32.0 T₂ 1637*   1638*   1632*   1621*   1626*   1623*   1625*   1630*   T₄1197*   1197*   1187*   1189*   1189*   1189*   1189*   1192*   C_(R) 1.7* 1.7  2.2*  1.3*  2.0*  1.5*  1.9*  1.7* Acid  0.09*  0.07  0.08* 0.09*  0.09*  0.09*  0.08*  0.08* Resistance

TABLE 13 Ex. 97 98 99 100 101 102 103 104 SiO₂ 66.4  66.0  65.4  65.0 64.6  66.1  65.7  66.2  Al₂O₃ 7.7 7.7 7.7 7.7 7.7 7.7 8.0 8.0 Li₂O 0.40.2 0  0  0  0.9 1.1 0.9 Na₂O 10.0  10.0  9.8 9.3 8.8 10.0  10.0  10.0 K₂O 0.8 0.7 0.7 1.0 1.3 0.5 0.4 0.5 MgO 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5CaO 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 TiO₂ 1.6 2.2 3.2 3.9 4.5 1.6 1.6 1.1ZrO₂ 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 R₂0 11.2  10.9  10.6  10.3  10.1 11.4  11.5  11.5  Li₂0/R₂0  0.04  0.02 0  0  0   0.08  0.09  0.08Na₂0/R₂0  0.89  0.91  0.93  0.90  0.88  0.88  0.87  0.87 K₂0/R₂0  0.07 0.07  0.07  0.10  0.12  0.04  0.04  0.05 d  2.53  2.55  2.54  2.56 2.56  2.54  2.54  2.53 α 65   64   65   65   65   65   64   64   E81.2  81.0  81.2  81.3  81.3  81.9  82.4  81.9  Tg 643   661   653  668   671   635   631   637   T_(L) ≦1151      1153    1170    1191   1220    1148    1162    1169    E/d 32.0  31.8  32.0  31.8  31.8  32.3 32.5  32.4  T₂ 1626*   1624*   1621*   1619*   1618*   1614*   1609*  1622*   T₄ 1191*   1191*   1192*   1193*   1193*   1181*   1178*  1187*   C_(R)  1.4*  1.1*  0.8*  0.6*  0.5*  1.4*  1.3*  1.4* Acid 0.09*  0.10*  0.10*  0.11*  0.12*  0.09*  0.10*  0.10* Resistance

TABLE 14 Ex. 105 106 107 108 109 110 111 112 SiO₂ 66.7  66.5  66.5 66.5  66.0  64.0  66.5  66.2  Al₂O₃ 8.0 7.5 7.5 7.5 7.5 7.5 7.5 8.5 Li₂O0.8 0.5 1.0 3.0 1.0 3.0 3.0 0.8 Na₂O 10.0  7.0 6.5 4.5 7.0 7.0 2.5 10.0 K₂O 0.9 2.5 2.5 2.5 2.5 2.5 4.5 0.9 MgO 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5CaO 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 TiO₂ 0.5 3.0 3.0 3.0 3.0 3.0 3.0 0.5ZrO₂ 1.7 1.5 1.5 1.5 1.5 1.5 1.5 1.7 R₂0 11.6  10.0  10.0  10.0  10.5 12.5  10.0  11.6  Li₂0/R₂0  0.07  0.05  0.10  0.30  0.10  0.24  0.30 0.07 Na₂0/R₂0  0.86  0.70  0.65  0.45  0.67  0.56  0.25  0.86 K₂0/R₂0 0.07  0.25  0.25  0.25  0.24  0.20  0.45  0.07 d  2.52  2.53  2.53 2.53  2.54  2.55  2.53  2.53 α 64   63   64   59   65   66   63   63  E 81.5  81.3  82.2  84.7  82.3  84.9  83.0  81.4  Tg 643   659   648  626   642   598   634   656   T_(L) 1150    ≦1190      ≦1191     1200    1151    ≦1145      ≧1222      E/d 32.3  32.1  32.5  33.5  32.4 33.2  32.9  32.1  T₂ 1632*   1654*   1649*   1627*   1635*   1557*  1648*   1636*   T₄ 1193*   1214*   1209*   1189*   1199*   1137*  1207*   1198*   C_(R)  1.7*  0.9*  0.9*  0.9*  0.9*  1.4*  0.9*  1.4*Acid  0.09*  0.09*  0.09*  0.09*  0.09*  0.12*  0.09*  0.11* Resistance

TABLE 15 Ex. 113 114 115 116 117 118 119 120 SiO₂ 65.7  65.2  64.7 66.3  64.7  66.0  66.0  66.0  Al₂O₃ 9.0 9.5 10.0  5.5 5.5 5.5 5.5 5.5Li₂O 0.7 0.7 0.7 0.1 2.7 9.9 9.5 11.0  Na₂O 10.0  10.0  10.0  10.0 10.0  4.0 2.5 0  K₂O 0.9 0.9 0.9 1.2 0.2 3.1 5.0 6.0 MgO 7.5 7.5 7.5 7.57.5 8.0 8.0 8.0 CaO 4.0 4.0 4.0 6.0 6.0 0  0  0  TiO₂ 0.5 0.5 0.5 1.41.4 1.0 1.0 1.0 ZrO₂ 1.7 1.7 1.7 2.0 2.0 2.5 2.5 2.5 R₂0 11.6  11.6 11.6  11.3  12.9  17.0  17.0  17.0  Li₂0/R₂0  0.06  0.06  0.06  0.01 0.21  0.58  0.56  0.65 Na₂0/R₂0  0.86  0.86  0.86  0.88  0.78  0.24 0.15 0  K₂0/R₂0  0.07  0.07  0.07  0.10  0.01  0.18  0.29  0.35 d  2.53 2.53  2.53  2.56  2.57  2.51  2.51  2.50 α 64   64   63   67   67  67   68   65   E 81.8  82.2  82.3  78.8  85.4  86.3  84.3  83.7  Tg643   651   654   625   592   541   544   552   T_(L) ≧1195     ≧1191      ≧1193      ≧1150      ≧1150      E/d 32.4  32.5  32.5  30.8 33.2  34.3  33.6  33.5  T₂ 1641*   1645*   1649*   1557*   1473*  1465*   1489*   1483*   T₄ 1204*   1208*   1213*   1143*   1075*  1041*   1062*   1056*   C_(R)  1.1*  0.9*  0.7*  2.5*  3.6* 19.5  15.1 21.5  Acid  0.12*  0.14*  0.16*  0.07*  0.08*  0.09  0.07*  0.08Resistance

TABLE 16 Ex. 121 122 123 124 125 126 127 128 SiO₂ 66.0  64.5 65.4 65.4 60.0  66.0  70.0  62.0  Al₂O₃ 5.5 12.0 8.6 8.6 15.0  5.5 3.5 8.5 Li₂O15.3  12.8 12.5 12.5  9.0 10.2  4.0 5.5 Na₂O 1.7 5.5 10.5 10.5  9.0 6.85.0 7.0 K₂O 0  3.4 0 0  2.0 0  5.0 8.0 MgO 8.0 0 0 0  5.0 8.0 8.0 6.5CaO 0  0 0 0  0  0  0  0  SrO 0  0 0 0  0  0  0  0  BaO 0  0 0 0  0  0 0  0  TiO₂ 1.0 0 0 0  0  1.0 3.0 1.0 ZrO₂ 2.5 1.8 3.0 3.0 0  2.5 1.5 1.5R₂0 17.0  21.7 23.0 23.0  20.0  17.0  14.0  20.5  Li₂0/R₂0  0.90 0.590.54  0.54  0.45  0.60  0.29  0.27 Na₂0/R₂0  0.10 0.25 0.46  0.46  0.45 0.40  0.36  0.34 K₂0/R₂0 0  0.16 0 0   0.10 0   0.36  0.39 d  2.51 2.47 2.50  2.46*  2.52*  2.49*  2.51* α 57   74 75   74*  64*  68*  87*  E91.5  82.7 85.6  83.2* 87.8* 80.1* 77.8* Tg 543   523 504   550*  543*   564*   525*   T_(L) ≧1050      1050 E/d 36.5  33.5 34.2  33.8*34.8* 32.1* 31.0* T₂ 1374*   1594 1454*   1573*   1430*   1598*  1537*   T₄ 958*   1093 998*   1111*   1011*   1140*   1102*   C_(R)24.6  3.2 3.5 18.3  3.6 10.0* 11.7*  6.6* Acid  0.07* 0.25  0.05 181   0.07*  0.03*  0.19* resistance

TABLE 17 Ex. 129 130 131 132 133 134 135 136 SiO₂ 63.0  63.0  63.0 63.2  60.0  70.0  68.0  66.0  Al₂O₃ 9.5 9.5 9.5 7.0 10.0  2.5 7.8 10.0 Li₂O 0.5 6.0 6.0 3.0 7.0 5.0 1.0 5.0 Na₂O 18.0  0  6.5 9.0 8.5 5.0 7.05.5 K₂O 0  12.5  6.5 6.0 6.0 5.0 11.0  0  MgO 6.5 6.5 8.5 5.0 8.0 8.03.0 5.0 CaO 0  0  0  1.8 0  0  0  4.0 SrO 0  0  0  0.1 0  0  0  0  BaO0  0  0  0.1 0  0  0  0  TiO₂ 1.0 1.0 0  3.0 0  3.0 1.0 3.0 ZrO₂ 1.5 1.50  1.8 0.5 1.5 1.2 1.5 R₂0 18.5  18.5  19.0  18.0  21.5  15.0  19.0 10.5  Li₂0/R₂0  0.03  0.32  0.32  0.17  0.33  0.33  0.05  0.48 Na₂0/R₂0 0.97 0   0.34  0.50  0.40  0.33  0.37  0.52 K₂0/R₂0 0   0.68  0.34 0.33  0.28  0.33  0.58 0  d  2.53*  2.49*  2.46*  2.55*  2.49*  2.49* 2.47*  2.53* α 83*  82*  81*  78*  87*  70*  90*  53*  E 79.5* 76.4*78.5* 78.6* 79.5* 80.3* 70.5* 86.5* Tg 567*   549*   526*   526*  509*   544*   538*   635*   T_(L) E/d 31.4* 30.7* 32.0* 30.8* 32.0*32.2* 28.6* 34.2* T₂ 1572*   1643*   1557*   1544*   1479*   1551*  1739*   1643*   T₄ 1133*   1189*   1109*   1114*   1053*   1099*  1241*   1189*   C_(R)  3.9*  2.7* 11.6*  3.9* 10.6* 21.5*  8.9*  0.5*Acid  0.19*  0.19*  0.19*  0.13*  0.32*  0.02*  0.07*  0.13* resistance

TABLE 18 Ex. 137 138 SiO₂ 63.0  63.0  Al₂O₃ 7.5 7.5 Li₂O 5.9 5.9 Na₂O11.3  11.3  K₂O 0  0  MgO 6.7 6.7 TiO₂ 3.0 2.5 ZrO₂ 1.5 1.5 B₂O₃ 1.0 1.5R₂O 17.3  17.3  Li₂0/R₂0  0.34  0.34 Na₂0/R₂0  0.66  0.66 K₂0/R₂0 0  0 d  2.53  2.52 α 71   70   E 84.2  83.8  Tg 543    541    T_(L) E/d 33.3 33.2  T₂ 1473*    1472*    T₄ 1044*    1040*    C_(R) 5*  5*  Acidresistance  0.14*  0.14*

TABLE 19 Ex. 1 2 3 4 5 6 7 8 SiO₂ 64.7 63.8 65.4 64.3 63.1 61.7 63.363.0 Al₂O₃ 9.2 9.0 9.3 9.1 10.7 12.3 9.0 8.9 Li₂O 4.1 4.0 4.1 4.1 4.14.0 2.6 3.1 Na₂O 4.0 4.0 4.1 4.0 5.0 5.0 6.8 3.9 K₂O 7.1 7.0 7.1 7.0 7.06.9 6.9 9.7 MgO 5.3 5.2 5.3 5.2 5.2 5.2 5.1 5.1 TiO₂ 2.6 0.0 4.6 1.3 0.00.0 1.3 1.3 ZrO₂ 3.0 6.9 0.0 5.0 5.0 4.9 4.9 4.9

TABLE 20 Ex. 9 10 11 12 13 14 15 16 SiO₂ 63.4 66.1 63.0 63.0 65.9 64.763.6 63.0 Al₂O₃ 9.0 9.1 8.9 8.9 9.3 9.2 9.0 8.9 Li₂O 2.4 3.6 2.7 4.0 4.22.5 1.6 1.6 Na₂O 7.9 3.5 5.6 0.0 8.8 12.0 11.8 10.0 K₂O 5.9 6.2 8.5 12.70.0 0.0 2.6 5.1 MgO 5.2 5.2 5.1 5.1 5.4 5.3 5.2 5.1 TiO₂ 1.3 1.3 1.3 1.31.3 1.3 1.3 1.3 ZrO₂ 4.9 5.0 4.9 4.9 5.1 5.0 4.9 4.9

TABLE 21 Ex. 17 18 19 20 21 22 23 24 SiO₂ 63.6 62.4 62.8 61.8 62.2 61.661.9 62.4 Al₂O₃ 9.0 9.1 12.5 12.5 12.6 14.1 12.5 12.6 Li₂O 0.8 4.6 3.93.2 2.9 4.1 3.8 2.9 Na₂O 15.2 4.5 11.1 11.4 11.6 10.1 10.1 11.6 K₂O 0.07.9 0.0 0.0 0.0 0.9 1.0 0.0 MgO 5.2 5.2 4.6 6.0 6.8 3.9 5.0 6.8 TiO₂ 1.31.3 0.0 0.0 0.0 3.2 2.6 0.7 ZrO₂ 4.9 5.0 5.0 5.0 4.0 2.0 3.0 3.0

TABLE 22 Ex. 25 26 27 28 29 30 31 32 SiO₂ 62.6 62.8 61.8 61.4 61.0 67.961.4 63.0 Al₂O₃ 12.6 12.7 12.5 12.4 12.3 9.1 8.7 8.9 Li₂O 2.9 2.9 2.92.9 2.9 3.1 0.8 0.0 Na₂O 11.6 11.7 11.5 11.4 11.3 3.1 8.2 16.8 K₂O 0.00.0 0.0 0.0 0.0 5.4 9.9 0.0 MgO 6.8 6.8 5.7 5.0 4.4 5.2 5.0 5.1 TiO₂ 1.32.0 2.6 3.9 5.1 1.3 1.2 1.3 ZrO₂ 2.0 1.0 3.0 3.0 3.0 5.0 4.8 4.9

TABLE 23 Ex. 33 34 35 36 37 38 39 40 SiO₂ 60.4 61.7 59.2 60.4 63.0 63.462.2 62.8 Al₂O₃ 8.5 8.7 8.4 8.5 17.9 16.3 18.1 16.7 Li₂O 0.0 0.0 0.0 1.91.4 0.0 2.3 2.3 Na₂O 8.0 12.3 3.9 0.0 13.3 13.9 12.0 12.1 K₂O 12.2 6.217.9 18.3 0.0 0.0 0.0 0.0 MgO 4.9 5.0 4.8 4.9 4.3 6.4 5.3 6.1 TiO₂ 1.21.2 1.2 1.2 0.0 0.0 0.0 0.0 ZrO₂ 4.7 4.8 4.6 4.7 0.0 0.0 0.0 0.0

TABLE 24 Ex. 41 42 43 44 45 46 47 48 SiO₂ 63.2 63.4 63.0 63.5 63.3 62.961.8 63.0 Al₂O₃ 15.9 15.8 15.9 15.3 15.4 15.8 16.4 13.4 Li₂O 2.4 1.9 2.02.6 2.7 2.7 2.8 2.8 Na₂O 11.7 12.2 12.5 11.8 11.8 11.8 11.4 11.7 K₂O 0.00.0 0.0 0.0 0.0 0.0 0.0 0.0 MgO 6.8 6.7 6.7 6.8 6.8 6.8 4.7 6.1 TiO₂ 0.00.0 0.0 0.0 0.0 0.0 0.0 0.0 ZrO₂ 0.0 0.0 0.0 0.0 0.0 0.0 3.0 3.0

TABLE 25 Ex. 49 50 51 52 53 54 55 56 SiO₂ 59.5 59.4 59.4 59.6 58.7 60.059.2 59.3 Al₂O₃ 14.2 14.2 14.2 14.2 14.0 14.3 14.1 14.2 Li₂O 1.2 1.4 1.61.4 1.4 1.4 1.4 1.4 Na₂O 4.3 4.3 4.3 3.4 0.9 3.9 4.3 2.4 K₂O 7.3 8.0 8.77.3 11.5 5.9 6.5 8.7 MgO 4.1 4.0 4.0 4.1 4.0 4.4 4.3 4.2 CaO 4.8 3.9 3.04.8 4.3 4.8 2.6 4.5 TiO₂ 1.9 1.9 1.9 2.5 2.4 2.5 3.7 2.5 ZrO₂ 2.9 2.92.9 2.9 2.8 2.9 3.8 2.9

TABLE 26 Ex. 57 58 59 60 61 62 63 64 SiO₂ 58.9 58.2 57.0 56.8 59.3 58.259.7 58.1 Al₂O₃ 14.1 14.1 14.8 14.0 11.0 13.9 14.3 13.9 Li₂O 1.6 1.8 1.81.6 1.6 1.6 1.6 0.7 Na₂O 2.4 2.4 2.4 2.4 2.4 2.3 2.4 2.3 K₂O 8.7 8.7 9.48.6 8.7 8.6 8.8 8.5 MgO 4.3 4.7 4.6 4.3 4.4 3.1 4.4 4.3 CaO 2.6 2.6 2.62.6 2.6 2.5 2.6 2.5 TiO₂ 3.7 3.7 3.7 6.1 6.2 6.0 6.2 6.0 ZrO₂ 3.8 3.83.8 3.8 3.8 3.7 0.0 3.7

TABLE 27 Ex. 65 66 67 68 69 70 71 72 SiO₂ 58.6 59.2 61.6 61.4 61.1 61.361.3 61.3 Al₂O₃ 14.0 14.1 11.1 11.1 12.5 12.5 11.9 11.8 Li₂O 1.6 1.6 1.61.6 1.4 1.4 1.6 1.4 Na₂O 0.5 2.4 2.4 2.4 3.4 3.4 2.3 3.4 K₂O 8.6 5.8 8.88.8 7.3 7.4 8.2 8.4 MgO 4.3 4.3 4.4 3.7 3.7 3.7 3.7 4.0 CaO 2.6 2.6 2.62.6 2.6 2.6 2.6 3.0 TiO₂ 6.1 6.1 3.7 5.6 4.7 4.8 5.6 2.5 ZrO₂ 3.8 3.83.8 2.9 3.3 2.9 2.9 4.2

TABLE 28 Ex. 73 74 75 76 77 78 79 80 SiO₂ 61.3 63.1 63.0 63.5 64.1 61.561.7 61.9 Al₂O₃ 11.8 11.9 11.8 12.0 12.0 11.9 11.9 11.9 Li₂O 1.2 0.1 0.80.0 0.1 0.0 0.1 0.9 Na₂O 3.8 7.3 3.0 9.7 9.1 9.6 9.6 6.8 K₂O 8.5 4.6 8.72.5 3.3 5.7 4.7 6.5 MgO 4.1 4.1 4.0 4.1 4.1 4.1 4.1 4.1 CaO 3.9 3.5 3.53.5 3.5 3.5 3.5 3.5 TiO₂ 1.2 2.1 1.9 1.5 0.4 0.4 1.0 1.0 ZrO₂ 4.2 3.43.3 3.4 3.4 3.3 3.4 3.4

TABLE 29 Ex. 81 82 83 84 85 86 87 88 SiO₂ 61.7 62.0 61.7 62.8 62.8 63.162.9 62.7 Al₂O₃ 11.9 12.0 11.8 11.9 11.9 12.0 12.0 12.2 Li₂O 0.7 1.1 0.70.5 0.4 0.6 0.5 0.3 Na₂O 6.7 6.8 6.8 6.8 6.8 6.8 6.8 8.5 K₂O 6.1 6.8 5.66.3 6.0 5.4 5.8 3.3 MgO 4.1 4.1 4.0 4.4 4.4 4.4 4.4 4.7 CaO 3.5 3.5 3.53.5 3.9 4.0 3.9 3.5 TiO₂ 2.1 0.4 2.9 0.4 0.4 0.4 0.4 1.3 ZrO₂ 3.4 3.43.1 3.4 3.4 3.4 3.3 3.4

TABLE 30 Ex. 89 90 91 92 93 94 95 96 SiO₂ 62.9 63.1 63.4 62.7 63.0 63.163.6 63.5 Al₂O₃ 12.3 12.3 12.2 12.3 12.3 12.3 12.4 12.3 Li₂O 0.3 0.3 0.60.1 0.5 0.2 0.3 0.3 Na₂O 8.5 8.5 8.8 9.8 8.5 9.8 9.8 9.8 K₂O 3.3 3.3 3.01.1 3.3 1.1 1.2 1.2 MgO 4.4 4.4 4.2 4.8 4.8 4.8 4.8 4.8 CaO 4.0 4.0 3.54.0 3.5 4.0 4.0 3.5 TiO₂ 1.3 1.3 1.2 2.0 0.6 1.4 0.6 1.3 ZrO₂ 3.1 2.93.1 3.3 3.4 3.3 3.3 3.3

TABLE 31 Ex. 97 98 99 100 101 102 103 104 SiO₂ 62.9 62.4 61.6 61.0 60.462.9 62.5 63.0 Al₂O₃ 12.3 12.3 12.2 12.2 12.1 12.4 12.9 12.9 Li₂O 0.20.1 0.0 0.0 0.0 0.1 0.5 0.4 Na₂O 9.8 9.8 9.6 9.0 8.5 9.8 9.8 9.8 K₂O 1.21.1 1.1 1.5 1.8 0.7 0.6 0.8 MgO 4.8 4.8 4.7 4.7 4.7 4.8 4.8 4.8 CaO 3.53.5 3.5 3.5 3.5 3.6 3.6 3.6 TiO₂ 2.0 2.8 4.0 4.8 5.6 2.0 2.0 1.4 ZrO₂3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3

TABLE 32 Ex. 105 106 107 108 109 110 111 112 SiO₂ 63.4 62.5 62.6 63.362.2 60.8 62.6 62.7 Al₂O₃ 12.9 12.0 12.0 12.1 12.0 12.1 12.0 13.7 Li₂O0.4 0.2 0.5 1.4 0.5 1.4 1.4 0.4 Na₂O 9.8 6.8 6.3 4.4 6.8 6.9 2.4 9.8 K₂O1.3 3.7 3.7 3.7 3.7 3.7 6.6 1.3 MgO 4.8 4.7 4.7 4.8 4.7 4.8 4.7 4.8 CaO3.5 3.5 3.5 3.6 3.5 3.5 3.5 3.5 TiO₂ 0.6 3.7 3.8 3.8 3.8 3.8 3.8 0.6ZrO₂ 3.3 2.9 2.9 2.9 2.9 2.9 2.9 3.3

TABLE 33 Ex. 113 114 115 116 117 118 119 120 SiO₂ 62.0 61.4 60.7 63.563.1 65.3 64.5 64.7 Al₂O₃ 14.4 15.2 15.9 8.9 9.1 9.2 9.1 9.1 Li₂O 0.30.3 0.3 0.1 1.3 4.9 4.6 5.4 Na₂O 9.7 9.7 9.7 9.9 10.1 4.1 2.5 0.0 K₂O1.3 1.3 1.3 1.7 0.3 4.8 7.7 9.2 MgO 4.7 4.7 4.7 4.8 4.9 5.3 5.2 5.3 CaO3.5 3.5 3.5 5.4 5.5 0.0 0.0 0.0 TiO₂ 0.6 0.6 0.6 1.8 1.8 1.3 1.3 1.3ZrO₂ 3.3 3.3 3.3 3.9 4.0 5.1 5.0 5.0

TABLE 34 Ex. 121 122 123 124 125 126 127 128 SiO₂ 68.4 60.9 63.4 63.456.8 66.4 67.7 57.6 Al₂O₃ 9.7 19.2 14.1 14.1 24.1 9.4 5.7 13.4 Li₂O 7.96.0 6.0 6.0 4.2 5.1 1.9 2.5 Na₂O 1.8 5.4 10.5 10.5 8.8 7.1 5.0 6.7 K₂O0.0 5.0 0.0 0.0 3.0 0.0 7.6 11.6 MgO 5.6 0.0 0.0 0.0 3.2 5.4 5.2 4.0 CaO0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SrO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 BaO0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 TiO₂ 1.4 0.0 0.0 0.0 0.0 1.3 3.9 1.2ZrO₂ 5.3 3.5 6.0 6.0 0.0 5.2 3.0 2.9

TABLE 35 Ex. 129 130 131 132 133 134 135 136 SiO₂ 59.0 57.0 60.2 58.357.1 68.5 60.7 62.7 Al₂O₃ 15.1 14.6 15.4 11.0 16.2 4.2 11.8 16.1 Li₂O0.2 2.7 2.8 1.4 3.3 2.4 0.4 2.4 Na₂O 17.4 0.0 6.4 8.6 8.3 5.0 6.4 5.4K₂O 0.0 17.7 9.7 8.7 9.0 7.7 15.4 0.0 MgO 4.1 3.9 5.4 3.1 5.1 5.3 1.83.2 CaO 0.0 0.0 0.0 1.5 0.0 0.0 0.0 3.5 SrO 0.0 0.0 0.0 0.2 0.0 0.0 0.00.0 BaO 0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 TiO₂ 1.2 1.2 0.0 3.7 0.0 3.9 1.23.8 ZrO₂ 2.9 2.8 0.0 3.4 1.0 3.0 2.2 2.9

TABLE 36 Ex. 137 138 SiO₂ 61.1 61.1 Al₂O₃ 12.3 12.4 Li₂O 2.9 2.9 Na₂O11.4 11.4 K₂O 0.0 0.0 MgO 4.4 4.4 TiO₂ 3.9 3.2 ZrO₂ 3.0 3.0 B₂O₃ 1.1 1.7

INDUSTRIAL APPLICABILITY

The glass of the present invention can be used for a glass substrate fora magnetic disk.

The entire disclosures of Japanese Patent Application No. 2009-090104filed on Apr. 2, 2009 and Japanese Patent Application No. 2010-030190filed on Feb. 15, 2010 including specifications, claims, drawings andsummaries are incorporated herein by reference in their entireties.

1. Glass for an information recording medium substrate, which comprises,as represented by mol % based on the following oxides, from 61 to 72% ofSiO₂, from 3 to 12% of Al₂O₃, from 0 to 14.3 of Li₂O, from 0 to 22% ofNa₂O, from 0 to 22% of K₂O, from 4 to 13% of MgO, from 0 to 6% of TiO₂and from 0 to 5% of ZrO₂, provided that the total content of Li₂O, Na₂Oand K₂O (R₂O) is from 8 to 22%, the ratio of the content of Li₂O to R₂O(Li₂O/R₂O) is at most 0.52, the ratio of the content of Na₂O to R₂O(Na₂O/R₂O) is at least 0.35, or the ratio of the content of K₂O to R₂O(K₂O/R₂O) is at least 0.45.
 2. The glass for an information recordingmedium substrate according to claim 1, wherein the ratio of Li₂O/R₂O isat most 0.5, or the ratio of Na₂O/R₂O is at least 0.4.
 3. The glass foran information recording medium substrate according to claim 1, whereinthe total content of TiO₂ and ZrO₂ (TiO₂+ZrO₂) is from 0 to 8%.
 4. Theglass for an information recording medium substrate according to claim1, which contains no B₂O₃ or contains less than 1% of B₂O₃.
 5. The glassfor an information recording medium substrate according to claim 1,wherein the difference obtained by deducting the content of Al₂O₃ fromthe content of SiO₂ exceeds 53%.
 6. The glass for an informationrecording medium substrate according to claim 1, wherein the differenceobtained by deducting the content of Li₂O from the content of K₂O is atmost 9%.
 7. The glass for an information recording medium substrateaccording to claim 1, wherein R₂O is at least 10%.
 8. The glass for aninformation recording medium substrate according to claim 1, whereinSiO₂ is from 62 to 71%, Al₂O₃ is from 4 to 12%, Li₂O is from 0 to 12.4%,Na₂O is from 0 to 20%, K₂O is from 0 to 19%, MgO is from 5 to 12%, TiO₂is from 0 to 5%, ZrO₂ is from 0 to 4%, and R₂O is from 11 to 20%.
 9. Theglass for an information recording medium substrate according to claim1, wherein the content of Al₂O₃ is at most 11%.
 10. The glass for aninformation recording medium substrate according to claim 1, whereinSiO₂ is from 63 to 70%, Al₂O₃ is from 5 to 9%, Li₂O is from 0 to 10.2%,Na₂O is from 0 to 19%, K₂O is from 0 to 12.8%, MgO is from 5 to 11%,TiO₂ is from 0 to 4%, ZrO₂ is from 0 to 4%, and R₂O is from 13 to 19%.11. The glass for an information recording medium substrate according toclaim 1, which contains neither CaO, SrO nor BaO.
 12. The glass for aninformation recording medium substrate according to claim 1, whichcontains at least one of CaO, SrO and BaO in the total content of atmost 3%.
 13. The glass for an information recording medium substrateaccording to claim 1, wherein Al₂O₃ is from 3 to 11%, Li₂O is from 0 toless than 5%, Na₂O is from 0 to 13%, K₂O is from 0 to 12%, MgO is from 4to 11%, R₂O is from 8 to 17%, and CaO is from more than 2% to 8%. 14.The glass for an information recording medium substrate according toclaim 1, wherein SiO₂ is from 61 to 71%, Al₂O₃ is from 4 to 11%, Li₂O isfrom 0 to 4.5%, Na₂O is from 0 to 12%, K₂O is from 0 to 10%, MgO is from4 to 9%, and CaO is from 2.5 to 7%.
 15. The glass for an informationrecording medium substrate according to claim 13, wherein ZrO₂ is from0.5 to 3%.
 16. The glass for an information recording medium substrateaccording to claim 1, which has a Young's modulus of at least 75 GPa anda specific modulus of at least 28 MNm/kg.
 17. The glass for aninformation recording medium substrate according to claim 1, which has aglass transition temperature of at least 500° C.
 18. The glass for aninformation recording medium substrate according to claim 13, which hasa Young's modulus of at least 76 GPa, a specific modulus of at least 30MNm/kg and a glass transition temperature of at least 590° C.
 19. Theglass for an information recording medium substrate according to claim1, which has an average linear expansion coefficient of at least56×10⁻⁷/° C. in a temperature range of from −50 to 70° C.
 20. The glassfor an information recording medium substrate according to claim 1,wherein (T_(L)−T₄)<50° C., where T_(L) is the liquidus temperature, andT₄ is the temperature at which the viscosity becomes 10⁴ dPa·s.
 21. Theglass for an information recording medium substrate according to claim1, which has a density of at most 2.60 g/cm³.
 22. A glass substrate foran information recording medium, which is made of the glass for aninformation recording medium substrate as defined in claim
 1. 23. Theglass substrate for an information recording medium according to claim22, wherein when immersed in 0.01 N nitric acid at 25° C., the etchingrate of glass is at most 0.3 nm/h.
 24. The glass substrate for aninformation recording medium according to claim 22, wherein when theglass is left under a steam atmosphere at 120° C. at 0.2 MPa for 20hours, C_(R)=C_(Li)+C_(Na)+C_(K) is at most 12 nmol/cm², where C_(Li),C_(Na) and C_(K) are the amounts of Li, Na and K which precipitate on asurface of the glass, respectively.
 25. A magnetic disk having amagnetic recording layer formed on the glass substrate for aninformation recording medium as defined in claim 22, 23 or 24.